The proposal is to study purine metabolism of the myocardium during and after a period of transient ischemia in dogs. The objective is to determine the feasibility of preserving and enhancing the replenishment of adenosine nucleotides during and after periods of ischemia by indirect biochemical manipulation of purine metabolism. This is acheived by the administration of allopurinol, 2-ethylamino-1,3,4-thiadiazole or an equimolar mixture of ATP and magnesium chloride before a period of ischemia. Preliminary evaluations of the agents are done in regional ischemic beating canine hearts. The ischemia is produced by occluding the left anterior descending coronary artery for a period. Blood samples are taken for the determination of uric acid, allantoin and CPK. Myocardial biopsies are taken at intervals for the determination of ATP, ADP and AMP. The metabolic studies are then extended to a canine cardiopulmonary bypass preparation. The myocardial ischemia is produced by cross-clamping the ascending aorta for a period. Blood samples and serial myocardial biopsies are taken for the biochemical determinations. The left ventricular function is evaluated in another group of dogs on cardiopulmonary bypass without myocardial biopsies.